The present invention relates to a method of controlling an automatic sheet feeder installed on an impact printer and, more particularly, to a method of controlling an automatic sheet feeder having a plurality of sheet hoppers to change feeding from the sheet hoppers automatically.
An automatic sheet feeder installed on an impact printer feeds sheets one at a time to the impact printer. When changing sheets having one width for sheets having a different width on such an automatic sheet feeder, the positions of sheet guides provided on a sheet hopper must be adjusted according to the width of the sheets. A recently developed automatic sheet feeder is provided with a plurality of sheet hoppers respectively containing sheets of different widths to feed selected sheets from the sheet hoppers.
FIG. 6 is a time chart showing the operation of an automatic sheet feeder provided with two sheet hoppers (hereinafter, referred to as a "dual hopper automatic sheet feeder") typical of conventional automatic sheet feeders provided with a plurality of sheet hoppers. A printer transmits a sheet hopper select signal 51 to the automatic sheet feeder for selecting either sheet hopper. A sheet delivery signal 52 commands the operation of a delivery roller, namely, a signal to drive a stepping motor provided in the automatic sheet feeder. Upon the reception of the sheet delivery signal 52, the automatic sheet feeder selects that sheet hopper corresponding to the hopper select signal 51, and drives the stepping motor to rotate the delivery roller for feeding a sheet from the selected sheet hopper to the printer.
Upon the detection of the sheet by a detector, not shown, the printer transmits a signal to the automatic sheet feeder to stop the sheet feeding operation, and then the automatic sheet feeder stops the stepping motor, thus stopping the sheet feeding operation. Indicated at 53 is a graph or line representing the sheet feeding speed of the automatic sheet feeder.
When a sheet feed command is given in a situation where the hopper select signal is not transmitted properly from the printer to the automatic sheet feeder, the sheet hopper specified previously and stored in the automatic sheet feeder is selected when the sheet feed command is given immediately after the automatic sheet feeder has been connected to a power source or the sheet hopper selected by the preceding hopper select command becomes active when the sheet feed command is given during operation.
This control method, however, requires one signal line for transmitting the hopper select signal 51 for selecting either sheet hopper, and another signal line for transmitting the sheet delivery signal 52 requesting feeding of a sheet. Once a host computer for controlling the printer has given a command for an initial resetting, the printer is unable to send a new hopper select signal to the automatic sheet feeder and, in some cases, the automatic sheet feeder selects the wrong sheet hopper.